1. Field of the Invention
This invention relates to a copper alloy having high strength, high electrical conductivity and good stampability. More particularly, the copper alloy contains controlled additions of magnesium, iron and phosphorous.
2. Description of Related Art
Elemental copper has a very high electrical conductivity and a relatively low strength. To be useful in commercial applications such as to be formed into leadframes or electrical connectors, copper is alloyed with various other elements, and combinations of elements, to increase strength. The alloying additions frequently impact other alloy properties. If the alloying additions are in solid solution with the copper, conductivity is frequently reduced. If the alloying additions result in large, hard, second phase particles, the surface finish of the copper alloy after cold rolling to sheet form may be marred by voids around these second phase particles. These voids can adversely affect the quality of an electrolytically deposited coating on the alloy. It is therefore, an objective to maximize the strength of a copper alloy without significantly degrading other desirable properties, such as uniform etching (in leadframe manufacture) and limited tool wear during stamping (in connecter manufacture).
Common alloying additions to copper include iron and phosphorous. An alloy designated by the Copper Development Association (CDA, Greenwich, Ct.) As copper alloy C19400 has the composition, by weight, of 2.1%-2.6% iron, 0.05%-0.20% zinc, 0.015%-0.15% phosphorous and the balance copper. Alloy C19400 has excellent stampability and an electrical conductivity of about 60% IACS (IACS stands for International Annealed Copper Standard and defines the conductivity of "pure" copper at 20.degree. C. As 100%). Another alloy, designated by the CDA as alloy C19210, has the composition, by weight, of 0.05%-0.15% iron, 0.025%-0.04% phosphorous and the balance copper. Alloy C19210 has an electrical conductivity of about 80% IACS, but relatively poor stampability.
Magnesium is sometimes added to copper-iron-phosphorous alloys. The magnesium combines with phosphorous to form a magnesium phosphide that precipitates from the copper matrix as a discrete second phase particulate. A dispersion of magnesium phosphide particulate throughout the copper alloy increases the strength of the copper alloy and, by effectively removing phosphorous from solid solution with the copper, increases electrical conductivity.
United States Patents that disclose a copper alloy containing iron, phosphorous and magnesium include U.S. Pat. No. 4,305,762 to Caron et al. and U.S. Pat. No. 4,605,532 to Knorr et al., both of which are incorporated by reference in their entireties herein.
The Caron et al. patent discloses a copper alloy containing 0.04%-0.20% of magnesium, phosphorous and iron. The Knorr et al. patent discloses a copper alloy containing 0.01%-0.20% magnesium, 0.1%-0.4% phosphorous, 0.3%-1.6% iron and the balance copper. Published Japanese Patent Application No. JP 58-199835 by Sumitomo Electric discloses a copper alloy that contains 0.03%-0.3% of magnesium, 0.03%-0.3% iron, 0.1%-0.3% phosphorous and the balance copper.
While copper alloys containing magnesium, phosphorous and iron are known, there remains a need for a copper alloy with an improved combination of electrical conductivity, strength and stampability.